Twin screw extruder

ABSTRACT

An extruder is disclosed, and more particularly, a twin screw extruder for mixing, compounding, kneading and/or extruding of materials. The twin screw extruder includes a barrel assembly having a housing. The twin screw extruder further includes a first screw provided within the housing and comprising threads. The twin screw extruder further includes a second screw provided within the housing and comprising a threaded portion and a shaft portion devoid of threads. A drive system which drives the first screw and the second screw.

FIELD OF THE INVENTION

The invention relates to an extruder and, more particularly, to a twin screw extruder for mixing, compounding, kneading and/or extruding of materials.

BACKGROUND OF THE INVENTION

Several techniques are available to process materials, including twin screw extruders and batch mixers. Twin screw extrusion is used extensively for mixing, compounding, reacting and extruding materials. For example, twin screw extruders can be used for processing many types of polymeric materials; although other materials can also be processed with twin screw extruders such as raw materials for food processing.

In operation, twin screw extruders have a profile for extrusion of thermally sensitive materials (e.g., PVC) and specialty polymer processing operations, such as compounding, devolatilization, chemical reactions, etc. Also, twin screw extruders exhibit improved processing capabilities. For example, twin screw extruders can have intermeshing or non-intermeshing screws along each of their entire length and throughout the housing, and can be designed as co-rotating or counter-rotating to achieve particular mixing characteristics. In this way, using intermeshing screws, the twin screw extruders can offer improved feeding and more positive conveying characteristics, which allow the machine to process hard-to-feed materials (e.g., powders, slippery materials, etc.). The twin screw extruders also yield short residence times and a narrow residence time distribution (RTD). Also, the twin screw extruders exhibit improved mixing, with larger heat transfer areas to allow improved control of stock temperatures.

SUMMARY OF THE INVENTION

In a first aspect of the invention, a twin screw extruder comprises a barrel assembly comprising a housing. The twin screw extruder further comprises a first screw provided within the housing and comprising threads. The twin screw extruder further comprises a second screw provided within the housing and comprising a threaded portion and a shaft portion devoid of threads. The twin screw extruder further comprises a drive system which drives the first screw and the second screw.

In another aspect of the invention, an extruder comprises a barrel assembly comprising a first section, a second section and a third section. The extruder further comprises a threaded screw provided only within the first section and the second section. The twin screw extruder further comprises a screw having a threaded portion provided only within the second section and the third section.

In yet another aspect of the invention, a method of mixing material comprises: placing material within a hopper assembly for feeding into a first compartment; transporting the material from the first compartment to a second compartment using a single threaded screw configuration; kneading the material in the second compartment with a twin screw configuration; and metering the material to a die with a single threaded screw configuration, different than the single threaded screw configuration used for transporting.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention.

FIG. 1 shows a perspective view of the twin screw extruder in accordance with aspects of the present invention;

FIG. 2 shows an exploded view of the screws the twin screw extruder in accordance with aspects of the present invention;

FIGS. 3 a, 3 b and 3 c show the respective compartments (e.g., sections) of the twin screw extruder in accordance with aspects of the present invention; and

FIGS. 4 a, 4 b and 4 c show alternative respective compartments (e.g., sections) of the twin screw extruder in accordance with aspects of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to an extruder and, more particularly, to a twin screw extruder for mixing, compounding, kneading and/or extruding of materials. In embodiments, the twin screw extruder of the present invention can be used as a compounder, mixer and a reactor. In embodiments, the twin screw extruder can be used for processing many types of materials. These materials can be, for example, polymeric and plastic materials, as well as raw materials for food processing. Of course, other material processes are also contemplated by the present invention. Also, advantageously, as described in more detail below, the twin screw extruder of the present invention significantly reduces material costs, and provides a simplified configuration, compared to conventional twin screw extruders.

More specifically, in the present invention, the twin screw extruder includes an alternating screw geometry (e.g., Z-shape), compared to a conventional parallel two screw configuration (e.g., U-shape). For example, in embodiments, the twin screw extruder of the present invention uses a screw to convey and transit molten materials, e.g., polymers, to the kneading section (transition zone); whereas, conventional twin screw extruders use two screws for providing this functionality. Accordingly, the conventional extruders have additional costs with regard to material costs, energy costs, etc., due to the need for twin screws along the entire system. Once the materials are conveyed to the kneading section, the twin screw extruder of the present invention uses two screws to knead, etc. the materials. At the end of the kneading process, a single screw then conveys the material to a die. In this way, the present configuration provides a single-twin-single screw configuration.

Accordingly and advantageously, the present invention provides a simplified design compared to existing complicated twin-screw extruders. That is, the present invention is able to significantly reduce material costs. Also, by using this simplified design, the present invention advantageously saves screw materials in the conveying and transition zones of the twin screw extruder, as well as simplifies the calculations required for calculating the flow rate of the material.

FIG. 1 shows a perspective view of the twin screw extruder in accordance with aspects of the present invention. More specifically, the twin screw extruder 10 includes a motor and drive system 15, for driving screws 20 a, 20 b housed within a barrel assembly 25. As described in more detail below, the barrel assembly 25 includes three compartments 25 a, 25 b and 25 c. As shown, in this exemplary configuration, the motor and drive system 15 includes a plurality of gears 30 driven by motor 35 which, in turn, drives the twin screws 20 a, 20 b. As one of ordinary skill in the art should understand, the motor and drive system 15 can have many different configurations, and can provide variable drive rates for the twin screws 20 a, 20 b. For example, the motor and drive system 15 can provide both co-rotation and counter-rotation of the twin screws 20 a, 20 b.

In embodiments, the barrel assembly 25 includes three separate, adjacent compartments (e.g., sections) 25 a, 25 b and 25 c. Specifically, compartment 25 a is a conveying compartment, which is used to convey material fed from a hopper and feed system 45 to the adjacent compartment 25 b. The compartment can also be used as a transition compartment. For example, heating of the material can begin in the compartment 25 a through, for example, shearing friction and/or heaters. The barrel assembly 25 also includes a kneading compartment 25 b, which is adjacent and in material flow communication with the conveying compartment 25 a. As described herein, material can be mixed, kneaded, heated, melted, etc. within the kneading compartment 25 b. A metering compartment 25 c is adjacent to and in material flow communication with the kneading compartment 25 b. The metering compartment 25 c will transit material to a die 50. As should be understood by those of skill in the art, the die 50 can include any combination of arrangements, for extruding different shapes.

As optional components, the barrel assembly 25 can include heaters 35, as well as a cooling system 40. The heaters 35 are designed to heat material conveyed and kneaded within the barrel assembly 25. This will assist in the shearing of the material, as should be understood by those of skill in the art. An optional vent and vacuum port 55 can also be provided on the barrel assembly 25, preferably at the compartment 25 c. The vent and vacuum port 55 can be used to vent gases from the melt.

As further shown in FIG. 1, the compartments 25 a, 25 b and 25 c include the screw components, in different configurations. More specifically, the conveying compartment 25 a includes a threaded portion of the screw 20 b (e.g., screw elements); whereas, the screw 20 a only has a shaft portion within the conveying compartment 25 a. More specifically, the screw 20 a in the conveying compartment 25 a is devoid of screw elements. In this way, the conveying compartment 25 a only includes a single screw configuration.

In the kneading compartment 25 b, both screws 20 a, 20 b are threaded (e.g., twin screw configuration), which can be intermeshed or non-meshed, depending on the specific configuration of the present invention. In embodiments, the screw pattern of the screws 20 a, 20 b can also include different thread configurations within the kneading compartment 25 b. For example, the screw pattern can be a kneading block screw element, as one illustrative, non-limiting example.

In the metering compartment 25 c, only the threaded screw 20 a is provided. In embodiments, to reduce material costs, the screw 20 b will not extend into the metering compartment 25 c, thus having its end terminating in the kneading compartment 25 b. In this way, the twin screw configuration of the present invention has a single-twin-single screw configuration.

FIG. 2 shows an exploded view of the screws 20 a, 20 b in accordance with aspects of the present invention. As shown in FIG. 2, screw 20 b has a length “X”, which is substantially fully threaded and is shorter than length “Y” of screw 20 a. As should be understood by those of skill in the art, the length “X” of screw 20 b corresponds to the length of the compartments 25 a, 25 b of FIG. 1; whereas, the length “Y” of screw 20 a corresponds to the length of the compartments 25 a, 25 b, 25 c of FIG. 1. In this way, the screw 20 b will not extend within the compartment 25 c.

Also, as shown in FIG. 2, the screw 20 a has a shaft portion 22 a (devoid of any thread elements) and a threaded portion 22 b. In embodiments, the shaft portion 22 a can be hollow, as it does no kneading, conveying, etc. of the material. In this way, additional material costs can be saved. As discussed above, the shaft portion 22 a will reside in the compartment 25 a of FIG. 1 with the threaded screw 22 b, so that only a single threaded screw is present, e.g., threaded portion of screw 20 b. On the other hand, the threaded portion 22 b of screw 20 a is configured to extend within the compartments 25 b, 25 c. In this way, threaded portions of the screws 20 a, 20 b will be provided in the compartment 25 b; whereas, only the threaded portion of the screw 20 a will be present in the compartment 25 c.

FIGS. 3 a, 3 b and 3 c show the respective compartments 25 a, 25 b, 25 c, in accordance with aspects of the present invention. As shown in these representations, the compartments are of a cylindrical shape. More specifically, FIG. 3 a shows an exploded view of compartment 25 a. As shown in this representation, the compartment 25 a includes a hole 25 a′, for accommodating the threaded screw 20 b. The compartment 25 a includes a hollow section 25 a″, for accommodating the shaft portion of the screw 20 a. As an example, the hollow section 25 a″ is only a cover. FIG. 3 b shows an exploded view of compartment 25 b. As shown in this representation, the compartment 25 a includes a two hole configuration 25 b′ (e.g., similar to a FIG. 8 design), for accommodating the threaded screw 20 b and the threaded portion 22 b of the screw 20 a. FIG. 3 c shows an exploded view of compartment 25 c. As shown in this representation, the compartment 25 c includes a single hole 25 c′, for accommodating the threaded portion 22 b of the screw 20 a. In embodiments, the section 25 c″ may be removed, as there is no screw in this portion of the machine.

FIGS. 4 a, 4 b and 4 c show alternative respective compartments 25 a, 25 b, 25 c, in accordance with aspects of the present invention. As shown in these representations, the compartments are of a rectangular or square shape. More specifically, FIG. 4 a shows an exploded view of compartment 25 a. As shown in this representation, the compartment 25 a includes a hole 25 a′, for accommodating the threaded screw 20 b. The compartment 25 a includes a hollow section 25 a″, for accommodating the shaft portion of the screw 20 a. As an example, the hollow section 25 a″ is only a cover. FIG. 4 b shows an exploded view of compartment 25 b. As shown in this representation, the compartment 25 a includes a two hole configuration 25 b′ (e.g., similar to a FIG. 8 design), for accommodating the threaded screw 20 b and the threaded portion 22 b of the screw 20 a. FIG. 4 c shows an exploded view of compartment 25 c. As shown in this representation, the compartment 25 c includes a single hole 25 c′, for accommodating the threaded portion 22 b of the screw 20 a. In embodiments, the section 25 c″ may be removed, as there is no screw in this portion of the machine.

In operation, material in the form of plastic pellets or powders, food, or other types of material are fed into the hopper and feed system 45, where they are conveyed and introduced into the compartment 25 a, and make contact with the single threaded screw 20 b. Depending on the operating conditions, materials will then transit to the melting zone, for polymers or plastics. It should be understood that the length/diameter (L/D) ratio of the threaded screw 20 b may vary depending on the material specifications. As should be understood by those of skill in the art, the L/D ratio is the ratio of the flighted length of the screw to its outside diameter. The materials will then be shifted to the compartment 25 b, transiting by way of the threaded screw 20 b. In the compartment 25 b, the material will be mixed, compounded, kneaded, etc. , via the twin screw configuration. The L/D ratio of the twin-screw section may also vary upon material specifications. The material will then pass to the compartment 25 c, comprising the single screw 20 a. Here, the material will be pushed outside of the extruder, through the die 50. The material can then be taken away by conventional take-off machinery (e.g., a pellitizer).

The foregoing examples have been provided for the purpose of explanation and should not be construed as limiting the present invention. While the present invention has been described with reference to an exemplary embodiment, changes may be made, within the purview of the appended claims, without departing from the scope and spirit of the present invention in its aspects. Also, although the present invention has been described herein with reference to particular materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. 

What is claimed is:
 1. A method of mixing material, comprising: placing material within a hopper assembly for feeding into a first compartment; transporting the material from the first compartment to a second compartment using a single threaded screw configuration; kneading the material in the second compartment with a twin screw configuration; and metering the material to a die with a single threaded screw configuration, different than the single threaded screw configuration used for transporting.
 2. The method of claim 1, wherein the metering the material to the die further comprises transporting the material through a third compartment with the single threaded screw configuration.
 3. The method of claim 2, further comprising venting gas using a vacuum port in the third compartment.
 4. The method of claim 1, further comprising heating or cooling the material in the first compartment.
 5. The method of claim 1, further comprising heating or cooling the material in the second compartment.
 6. The method of claim 1, further comprising placing at least one of polymeric material, raw materials, plastic materials, and food within the hopper assembly for the feeding into the first component.
 7. The method of claim 1, further comprising placing at least one of pellets and powders within the hopper assembly for the feeding into the first component.
 8. The method of claim 1, further comprising at least one of mixing, compounding, reacting, and extruding the material in the second compartment with the twin screw configuration. 